The present invention relates to improved overlay or bond coatings applied to materials used in the hot sections of modern gas turbine engines.
Thermal barrier coatings on a substrate alloy usually include a thermally insulating ceramic layer deposited over a metallic bond coat. Traditionally, thermal barrier coatings use yttria partially stabilized zirconia on a bond coat such as MCrAlY delivered by a low pressure plasma spray, air plasma, or physical vapor deposition method. A typical thermal barrier coating for a rotating airfoil application consists of the metallic bond coat over a single crystal casting of a nickel based alloy. On the bond coat, the thermally insulating layer is deposited typically by electron beam physical vapor deposition. The ceramic adheres to the bond coat through the formation of a thin, thermally grown oxide scale of aluminum oxide. During engine operation, the thermally grown oxide grows. Attendant with the growth of the oxide scale are increased thermally grown oxide residual stresses and bond coat creep.
Thus, there is needed an overlay bond coat which has improved strength, particularly creep strength, and which would lead to improved thermal barrier coating life.